The militant who led a deadly gun attack at a Saudi oil refinery on Saturday used to live in London and belonged to a British-based dissident group opposed to the ruling Saudi Royal Family.

Mustafa Abdel-Qader Abed al-Ansari carried out the weekend massacre with his brother and their two nephews in which two Britons and three other Westerners died.

The Saudi authorities said today that al-Ansari was a member of the dissident group called the Committee for the Defence of Legitimate Rights (CDLR).

Members of CDLR have confirmed that al-Ansari, who was shot dead by police after the attack, came to England in 1994 and joined the group at the age of 22 after fleeing his Saudi homeland.

He studied English for two years and even married an Englishwoman in Cambridge, but after the marriage failed he left England to fight with Muslim extremists in Afghanistan. He was on the FBI's most wanted list, and was also wanted for questioning in Riyadh.

He re-entered Saudi Arabia illegally to carry out the attack.

Mohammed al-Massari, the secretary general of the CDLR, said today that he remembered al-Ansari well, and thought he might have led the massacre in response to images of the torture of prisoners in Iraq. "He was a very good young man," said Mr al-Massari.

"He was a very staunch believer in Jihad. I thought he was more rational than (to use) desperado action."

Saturday's massacre was carried out by al-Ansari along with his brother, Ayman Abdel-Qader al-Ansari, and their two nephews, Samir Suleiman al-Ansari and Sami Suleiman al-Ansari.

The other three were employees at the oil refinery, who used their personnel cards to get in. They fired randomly at Saudi and Western employees at the oil installation in the Red Sea town of Yanbu, and tied the body of one of their American victims to the back of a car and dragged down the street past a school.

The British victims were Michael Hardy, 44, from Kent, and Michael McGillen, 52, from Stoke-on-Trent in Staffordshire. Two Americans, an Australian and a Saudi guard were also shot dead.

All four gunmen later died in a gun battle with police, in which two members of the Saudi security service were also killed and 20 wounded. Many Westerners have left the Kingdom since the killings.